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<div  id='write'  class = 'is-node'><div class='md-toc' mdtype='toc'><p class="md-toc-content"><span class="md-toc-item md-toc-h2" data-ref="n1148"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1148">1:正则表达式(理解)</a></span><span class="md-toc-item md-toc-h4" data-ref="n1149"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1149">(1)就是符合一定规则的字符串</a></span><span class="md-toc-item md-toc-h4" data-ref="n1150"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1150">(2)常见规则</a></span><span class="md-toc-item md-toc-h4" data-ref="n1221"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1221">(3)常见功能：(分别用的是谁呢?)</a></span><span class="md-toc-item md-toc-h6" data-ref="n1223"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1223">A:判断功能</a></span><span class="md-toc-item md-toc-h6" data-ref="n1328"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1328">B:分割功能</a></span><span class="md-toc-item md-toc-h6" data-ref="n1330"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1330">C:替换功能</a></span><span class="md-toc-item md-toc-h6" data-ref="n1332"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1332">D:获取功能</a></span><span class="md-toc-item md-toc-h4" data-ref="n1224"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1224">(4)案例</a></span><span class="md-toc-item md-toc-h2" data-ref="n1234"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1234">2:Math(掌握)</a></span><span class="md-toc-item md-toc-h4" data-ref="n1235"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1235">(1)针对数学运算进行操作的类</a></span><span class="md-toc-item md-toc-h4" data-ref="n1236"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1236">(2)常见方法(自己补齐)</a></span><span class="md-toc-item md-toc-h4" data-ref="n1253"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1253">(3)案例：</a></span><span class="md-toc-item md-toc-h2" data-ref="n1256"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1256">3:Random(理解)</a></span><span class="md-toc-item md-toc-h4" data-ref="n1257"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1257">(1)用于产生随机数的类</a></span><span class="md-toc-item md-toc-h4" data-ref="n1258"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1258">(2)构造方法:</a></span><span class="md-toc-item md-toc-h6" data-ref="n1259"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1259">A: <code>Random()</code> 默认种子，每次产生的随机数不同</a></span><span class="md-toc-item md-toc-h6" data-ref="n1260"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1260">B: <code>Random(long seed)</code> 指定种子，每次种子相同，随机数就相同</a></span><span class="md-toc-item md-toc-h4" data-ref="n1261"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1261">(3)成员方法:</a></span><span class="md-toc-item md-toc-h6" data-ref="n1262"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1262">A: <code>int nextInt()</code> 返回int范围内的随机数</a></span><span class="md-toc-item md-toc-h6" data-ref="n1263"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1263">B: <code>int nextInt(int n)</code> 返回[0,n)范围内的随机数</a></span><span class="md-toc-item md-toc-h2" data-ref="n1264"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1264">4:System(掌握)</a></span><span class="md-toc-item md-toc-h4" data-ref="n1265"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1265">(1)系统类,提供了一些有用的字段和方法</a></span><span class="md-toc-item md-toc-h4" data-ref="n1266"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1266">(2)成员方法(自己补齐)</a></span><span class="md-toc-item md-toc-h2" data-ref="n1268"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1268">5:BigInteger(理解)</a></span><span class="md-toc-item md-toc-h4" data-ref="n1269"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1269">(1)针对大整数的运算</a></span><span class="md-toc-item md-toc-h4" data-ref="n1270"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1270">(2)构造方法<span>	</span></a></span><span class="md-toc-item md-toc-h4" data-ref="n1272"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1272">(3)成员方法(自己补齐)</a></span><span class="md-toc-item md-toc-h2" data-ref="n1284"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1284">6:BigDecimal(理解)</a></span><span class="md-toc-item md-toc-h4" data-ref="n1285"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1285">(1)浮点数据做运算，会丢失精度。</a></span><span class="md-toc-item md-toc-h4" data-ref="n1287"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1287">(2)构造方法</a></span><span class="md-toc-item md-toc-h4" data-ref="n1289"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1289">(3)成员方法：</a></span><span class="md-toc-item md-toc-h2" data-ref="n1301"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1301">7:Date/DateFormat(掌握)</a></span><span class="md-toc-item md-toc-h4" data-ref="n1302"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1302">(1)Date是日期类，可以精确到毫秒。</a></span><span class="md-toc-item md-toc-h6" data-ref="n1303"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1303">A:构造方法</a></span><span class="md-toc-item md-toc-h6" data-ref="n1305"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1305">B:成员方法</a></span><span class="md-toc-item md-toc-h6" data-ref="n1307"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1307">C:日期和毫秒值的相互转换</a></span><span class="md-toc-item md-toc-h4" data-ref="n1309"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1309">(2)DateFormat</a></span><span class="md-toc-item md-toc-h6" data-ref="n1311"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1311">A:SimpleDateFormat(String pattern) </a></span><span class="md-toc-item md-toc-h6" data-ref="n1313"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1313">B:日期和字符串的转换</a></span><span class="md-toc-item md-toc-h6" data-ref="n1315"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1315">C:案例：</a></span><span class="md-toc-item md-toc-h2" data-ref="n1317"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1317">8:Calendar(掌握)</a></span><span class="md-toc-item md-toc-h4" data-ref="n1318"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1318">(1)日历类</a></span><span class="md-toc-item md-toc-h4" data-ref="n1320"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1320">(2)如何得到一个日历对象呢?</a></span><span class="md-toc-item md-toc-h4" data-ref="n1322"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1322">(3)成员方法</a></span><span class="md-toc-item md-toc-h6" data-ref="n1323"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1323">A:根据日历字段得到对应的值</a></span><span class="md-toc-item md-toc-h6" data-ref="n1324"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1324">B:根据日历字段和一个正负数确定是添加还是减去对应日历字段的值</a></span><span class="md-toc-item md-toc-h6" data-ref="n1325"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1325">C:设置日历对象的年月日</a></span><span class="md-toc-item md-toc-h4" data-ref="n1326"><a class="md-toc-inner" style="cursor: pointer;" href="#header-n1326">(4)案例：</a></span></p></div><h2><a name='header-n1148' class='md-header-anchor '></a>1:正则表达式(理解)</h2><h4><a name='header-n1149' class='md-header-anchor '></a>(1)就是符合一定规则的字符串</h4><h4><a name='header-n1150' class='md-header-anchor '></a>(2)常见规则</h4><figure><table><thead><tr><th style='text-align:center;' >ReExp</th><th style='text-align:right;' >含义</th></tr></thead><tbody><tr><td style='text-align:center;' >(字符)</td><td style='text-align:right;' >&nbsp;</td></tr><tr><td style='text-align:center;' >x</td><td style='text-align:right;' >字符 x。举例：&#39;a&#39;表示字符a</td></tr><tr><td style='text-align:center;' >\n</td><td style='text-align:right;' >新行（换行）符 (&#39;\u000A&#39;)</td></tr><tr><td style='text-align:center;' >\r</td><td style='text-align:right;' >回车符 (&#39;\u000D&#39;)</td></tr><tr><td style='text-align:center;' >(字符类)</td><td style='text-align:right;' >&nbsp;</td></tr><tr><td style='text-align:center;' >[abc]</td><td style='text-align:right;' >a、b 或 c（简单类）</td></tr><tr><td style='text-align:center;' >[^abc]</td><td style='text-align:right;' >任何字符，除了 a、b 或 c（否定）</td></tr><tr><td style='text-align:center;' >[a-zA-Z]</td><td style='text-align:right;' >a到 z 或 A到 Z，两头的字母包括在内（范围）</td></tr><tr><td style='text-align:center;' >[0-9]</td><td style='text-align:right;' >0到9的字符都包括v</td></tr><tr><td style='text-align:center;' >(预定义字符类)</td><td style='text-align:right;' >&nbsp;</td></tr><tr><td style='text-align:center;' >.</td><td style='text-align:right;' >任何字符。.字符本身，怎么表示呢? <code>\.</code></td></tr><tr><td style='text-align:center;' >\d</td><td style='text-align:right;' >数字：[0-9]</td></tr><tr><td style='text-align:center;' >\w</td><td style='text-align:right;' >单词字符：[a-zA-Z_0-9]</td></tr><tr><td style='text-align:center;' >(边界匹配器)</td><td style='text-align:right;' >&nbsp;</td></tr><tr><td style='text-align:center;' >^</td><td style='text-align:right;' >行的开头</td></tr><tr><td style='text-align:center;' >$</td><td style='text-align:right;' >行的结尾</td></tr><tr><td style='text-align:center;' >\b</td><td style='text-align:right;' >单词边界</td></tr></tbody></table></figure><p>Greedy 数量词 </p><ul><li>X? X，一次或一次也没有</li><li>X* X，零次或多次</li><li>X+ X，一次或多次</li><li>X{n} X，恰好 n 次 </li><li>X{n,} X，至少 n 次 </li><li>X{n,m} X，至少 n 次，但是不超过 m 次 </li></ul><h4><a name='header-n1221' class='md-header-anchor '></a>(3)常见功能：(分别用的是谁呢?)</h4><h6><a name='header-n1223' class='md-header-anchor '></a>A:判断功能</h6><p>String类的<code>public boolean matches(String regex)</code></p><h6><a name='header-n1328' class='md-header-anchor '></a>B:分割功能</h6><p>String类的<code>public String[] split(String regex)</code></p><h6><a name='header-n1330' class='md-header-anchor '></a>C:替换功能</h6><p>String类的<code>public String replaceAll(String regex,String replacement)</code></p><h6><a name='header-n1332' class='md-header-anchor '></a>D:获取功能</h6><p>Pattern和Matcher
<code>Pattern p = Pattern.compile(&quot;a*b&quot;);</code>
<code>Matcher m = p.matcher(&quot;aaaaab&quot;);</code>
<span>				</span>
<code>find()</code>:查找存不存在
<code>group()</code>:获取刚才查找过的数据</p><h4><a name='header-n1224' class='md-header-anchor '></a>(4)案例</h4><ul><li>A:判断电话号码和邮箱</li><li>B:按照不同的规则分割数据</li><li>C:把论坛中的数字替换为*</li><li>D:获取字符串中由3个字符组成的单词</li></ul><h2><a name='header-n1234' class='md-header-anchor '></a>2:Math(掌握)</h2><h4><a name='header-n1235' class='md-header-anchor '></a>(1)针对数学运算进行操作的类</h4><h4><a name='header-n1236' class='md-header-anchor '></a>(2)常见方法(自己补齐)</h4><ul><li>A:绝对值</li><li>B:向上取整</li><li>C:向下取整</li><li>D:两个数据中的大值</li><li>E:a的b次幂</li><li>F:随机数</li><li>G:四舍五入</li><li>H:正平方根</li></ul><h4><a name='header-n1253' class='md-header-anchor '></a>(3)案例：</h4><p>A:猜数字小游戏
B:获取任意范围的随机数</p><h2><a name='header-n1256' class='md-header-anchor '></a>3:Random(理解)</h2><h4><a name='header-n1257' class='md-header-anchor '></a>(1)用于产生随机数的类</h4><h4><a name='header-n1258' class='md-header-anchor '></a>(2)构造方法:</h4><h6><a name='header-n1259' class='md-header-anchor '></a>A: <code>Random()</code> 默认种子，每次产生的随机数不同</h6><h6><a name='header-n1260' class='md-header-anchor '></a>B: <code>Random(long seed)</code> 指定种子，每次种子相同，随机数就相同</h6><h4><a name='header-n1261' class='md-header-anchor '></a>(3)成员方法:</h4><h6><a name='header-n1262' class='md-header-anchor '></a>A: <code>int nextInt()</code> 返回int范围内的随机数</h6><h6><a name='header-n1263' class='md-header-anchor '></a>B: <code>int nextInt(int n)</code> 返回[0,n)范围内的随机数</h6><h2><a name='header-n1264' class='md-header-anchor '></a>4:System(掌握)</h2><h4><a name='header-n1265' class='md-header-anchor '></a>(1)系统类,提供了一些有用的字段和方法</h4><h4><a name='header-n1266' class='md-header-anchor '></a>(2)成员方法(自己补齐)</h4><p>A:运行垃圾回收器
B:退出jvm
C:获取当前时间的毫秒值
D:数组复制</p><h2><a name='header-n1268' class='md-header-anchor '></a>5:BigInteger(理解)</h2><h4><a name='header-n1269' class='md-header-anchor '></a>(1)针对大整数的运算</h4><h4><a name='header-n1270' class='md-header-anchor '></a>(2)构造方法<span>	</span></h4><p>A:<code>BigInteger(String s)</code></p><h4><a name='header-n1272' class='md-header-anchor '></a>(3)成员方法(自己补齐)</h4><ul><li>加</li><li>减</li><li>乘</li><li>除</li><li>商和余数</li></ul><h2><a name='header-n1284' class='md-header-anchor '></a>6:BigDecimal(理解)</h2><h4><a name='header-n1285' class='md-header-anchor '></a>(1)浮点数据做运算，会丢失精度。</h4><p>所以，针对浮点数据的操作建议采用BigDecimal。(金融相关的项目)</p><h4><a name='header-n1287' class='md-header-anchor '></a>(2)构造方法</h4><p>A:<code>igDecimal(String s)</code></p><h4><a name='header-n1289' class='md-header-anchor '></a>(3)成员方法：</h4><ul><li>加</li><li>减</li><li>乘</li><li>除</li><li>自己保留小数几位</li></ul><h2><a name='header-n1301' class='md-header-anchor '></a>7:Date/DateFormat(掌握)</h2><h4><a name='header-n1302' class='md-header-anchor '></a>(1)Date是日期类，可以精确到毫秒。</h4><h6><a name='header-n1303' class='md-header-anchor '></a>A:构造方法</h6><p><code>Date()</code>
<code>Date(long time)</code></p><h6><a name='header-n1305' class='md-header-anchor '></a>B:成员方法</h6><p><code>getTime()</code>
<code>setTime(long time)</code></p><h6><a name='header-n1307' class='md-header-anchor '></a>C:日期和毫秒值的相互转换</h6><p>案例：你来到这个世界多少天了?</p><h4><a name='header-n1309' class='md-header-anchor '></a>(2)DateFormat</h4><p>针对日期进行格式化和针对字符串进行解析的类，但是是抽象类，所以使用其子类SimpleDateFormat</p><h6><a name='header-n1311' class='md-header-anchor '></a>A:SimpleDateFormat(String pattern) </h6><p>给定模式
yyyy-MM-dd HH:mm:ss</p><h6><a name='header-n1313' class='md-header-anchor '></a>B:日期和字符串的转换</h6><p>a:Date -- String
<code>format()</code>
<span>		</span>
b:String -- Date
<code>parse()</code></p><h6><a name='header-n1315' class='md-header-anchor '></a>C:案例：</h6><p>制作了一个针对日期操作的工具类。</p><h2><a name='header-n1317' class='md-header-anchor '></a>8:Calendar(掌握)</h2><h4><a name='header-n1318' class='md-header-anchor '></a>(1)日历类</h4><p>封装了所有的日历字段值，通过统一的方法根据传入不同的日历字段可以获取值。</p><h4><a name='header-n1320' class='md-header-anchor '></a>(2)如何得到一个日历对象呢?</h4><p><code>Calendar rightNow = Calendar.getInstance();</code>
本质返回的是子类对象</p><h4><a name='header-n1322' class='md-header-anchor '></a>(3)成员方法</h4><h6><a name='header-n1323' class='md-header-anchor '></a>A:根据日历字段得到对应的值</h6><h6><a name='header-n1324' class='md-header-anchor '></a>B:根据日历字段和一个正负数确定是添加还是减去对应日历字段的值</h6><h6><a name='header-n1325' class='md-header-anchor '></a>C:设置日历对象的年月日</h6><h4><a name='header-n1326' class='md-header-anchor '></a>(4)案例：</h4><p>计算任意一年的2月份有多少天?</p></div>
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